Precipitation of multiple light elements to power Earth's early dynamo

Mittal, Tushar; Knezek, Nicholas; Arveson, S. M.; McGuire, C. P.; Williams, C. D.; Jones, T. D.; Li, Jie

doi:10.1016/j.epsl.2019.116030

Cited by 33 publications

(50 citation statements)

References 40 publications

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“…However, precipitation rates are still under debate (Badro et al, 2018;Du et al, 2019) and the power that is made available by precipitation depends strongly on the abundance and coupled partitioning behaviour of iron, silicon and magnesium oxides (Mittal et al, 2020).…”

Section: Introductionmentioning

confidence: 99%

On the Evolution of Thermally Stratified Layers at the top of Earth’s Core

Greenwood¹,

Mound²,

Davies³

2020

Preprint

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Stable stratification at the top of the Earth’s outer core has been suggested based upon seismic and geomagnetic observations, however, the origin of the layer is still unknown. In this paper we focus on a thermal origin for the layer and conduct a systematic study on the thermal evolution of the core. We develop a new numerical code to model the growth of thermally stable layers beneath the CMB, integrated into a thermodynamic model for the long term evolution of the core. We conduct a systematic study on plausible thermal histories using a range of core properties and, combining thickness and stratification strength constraints, investigate the limits upon the present day structure of the thermal layer. We find that whilst there are a number of scenarios for the history of the CMB heat flow, Qc, that give rise to thermal stratification, many of them are inconsistent with previously published exponential trends in Qc from mantle evolution models. Layers formed due to an exponentially decaying Qc are limited to 250-400 km thick and have maximum present-day Brunt-Va ̈isa ̈l ̈a periods, TBV = 8 − 24 hrs. When entrainment of the lowermost region of the layer is included in our model, the upper limit of the layer size is reduced and can fully inhibit the growth of any layer if our non-dimensional measure of entrainment, E > 0.2. The period TBV is insensitive to the evolution and so our estimates remain distinct from estimates arising from a chemical origin. Therefore, TBV should be able to discern between thermal and chemical mechanisms as improved seismic constraints are obtained.

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Section: Introductionmentioning

confidence: 99%

On the Evolution of Thermally Stratified Layers at the top of Earth’s Core

Greenwood¹,

Mound²,

Davies³

2020

Preprint

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show abstract

“…Much recent work has focused on the partitioning of Mg, Si and O between the core and mantle. Mg and Si are of interest because they may become saturated in the core as the planet cools, precipitating as oxides MgO and SiO 2 respectively, which releases gravitational energy that is available to power the geodynamo (O'Rourke and Stevenson, 2016;Badro et al, 2016;Hirose et al, 2017;Mittal et al, 2020). The study of FeO has attracted attention because it provides a mechanism for oxygen to enter the core, either from FeO in ferropericlase in the present Earth (Frost et al, 2010) or from an FeO-enriched basal magma ocean in the past (Davies et al, 2020), which leads to a stable stratification below the CMB (Buffett and Seagle, 2010;Davies et al, 2020).…”

Section: Bulk Composition Of the Core And Basal Magma Oceanmentioning

confidence: 99%

“…Du et al (2019) found that high heat flows and cooling rates were still required to drive the dynamo using precipitation rates of dw c M gO /dT = 6 × 10 −6 K −1 obtained from their experiments. Additional power provided by precipitation reduces the core cooling rate required to meet a given entropy production and hence predicts an older inner core age; however thermal history models with precipitation still predict supersolidus temperatures for the first ∼1 − 3 Gyr after core formation (O'Rourke et al, 2017;Mittal et al, 2020) and so suggest the existence of a BMO at least in early times.…”

Section: Chemical Precipitationmentioning

confidence: 99%

“…In this model the interaction layer evolution is governed by a balance between growth due to precipitation and erosion by mantle flow. Mittal et al (2020) found that a wide range of evolutionary scenarios are possible with different oxides precipitating at different times depending on the properties of the interaction layer (its thickness and erosion rate), the initial compositions and the parameters defining the equilibrium constants. This behaviour is consistent with the simple mass balance calculations presented in Section 3.…”

Section: Chemical Precipitationmentioning

confidence: 99%

“…DDD. This Case employs dissociation reactions for all three species as done byMittal et al (2020), with distribution coefficients given…”

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confidence: 99%

See 2 more Smart Citations

Thermo-Chemical Dynamics in Earth's Core Arising from Interactions with the Mantle

Davies¹,

Greenwood²

2021

Preprint

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Thermo-chemical interactions at the core-mantle boundary (CMB) play an integral role in determining the dynamics and evolution Earth's deep interior. This review considers the processes in the core that arise from heat and mass transfer at the CMB, with particular focus on thermo-chemical stratification and the precipitation of oxides. A fundamental parameter is the thermal conductivity of the core, which we estimate as k = 70 − 110 W m −1 K −1 at CMB conditions based on consistent extrapolation from a number of recent studies. These high conductivity values imply the existence of an early basal magma ocean (BMO) overlying a hot core and rapid cooling potentially leading to a loss of power to the dynamo before the inner core formed around 0.5 − 1 Gyrs ago, the so-called "new core paradox". Coupling core thermal evolution modelling and calculations of chemical equilibrium between liquid iron and silicate melts suggests that FeO dissolved into the core after its formation, creating a stably stratified chemical layer below the CMB, while precipitation of MgO and SiO 2 was delayed until the last 2−3 Gyrs and was therefore not available to power the early dynamo; however, once initiated, precipitation supplied ample power for field generation. We also present a possible solution to the new core paradox without requiring precipitation or radiogenic heating using k = 70 W m −1 K −1 . The model matches the present inner core size and heat flow and temperature at the top of the

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Dynamics in Earth's Core Arising from Thermo‐Chemical Interactions with the Mantle

Davies

Greenwood

2023

Geophysical Monograph Series

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Precipitation of multiple light elements to power Earth's early dynamo

Cited by 33 publications

References 40 publications

On the Evolution of Thermally Stratified Layers at the top of Earth’s Core

On the Evolution of Thermally Stratified Layers at the top of Earth’s Core

Thermo-Chemical Dynamics in Earth's Core Arising from Interactions with the Mantle

Dynamics in Earth's Core Arising from Thermo‐Chemical Interactions with the Mantle

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